Electrical resistor and method of making the same



April l1, 1950 DE HART G. scRAN-roM 2,503,418

ELECTRICAL RESISTOR AND METHOD OF MAKING THE SAME Filed June 20, 1947 Mrs/N701? 0. 6'. SC'RA NTOM ar Patented Apr. l1, 1950 ELECTRICAL RESISTOR AND METHOD 0F MAKING THE SAME De Hart G. Scrantom, Ma to Western Electric 15 Claims. l

This invention relates to electrical resistors and methods of making the same and more particularly to non-inductive carbon deposited resistors and methods of making the same.

Objects of this invention are to provide a new and eiiicient electrical resistor.

In accordance with one embodiment of this invention a non-inductive resistor may be made from a carbon coated tubular ceramic blank by cutting a pair of spiral grooves around the carbon coated blank to remove the conducting carbon from the grooved area, the grooves running ofi' one end of the blank to separate the termini of the conducting portions between the spiral grooves, and the grooves being stopped short of the other end of the blank to provide aconnecting carbon-covered surface between the parallel conducting paths. At that end to which the grooves extend, connectors such as wire pig-tails or strips of metal are secured to electrically contact the end of each parallel conducting path between the insulating grooves.

A complete understanding of the invention will be had by reference to the following'detailed description taken in conjunction with the accompanying drawing, in which Fig. 1 illustrates a method of cutting two spiral insulating grooves simultaneously with a double cutting element; v Fig. 2 illustrates another method by which two parallel insulating grooves may be cut simultaneously by two separate cutting elements on separate shafts Fig. 3 illustrates a method by which one cutting element may be used to iirst cut one groove and then cut the second parallel groove;

Fig. 4 shows a blank in which the parallel insulating grooves have been cut, the left end of the blank having been ground off to permit a separation of the parallel conducting paths in the resistive coating;

Fig. 5 illustrates a method of connecting electrical terminals to the ends of the conducting paths of the resistor; and

Fig. 6 is an enlarged cross-sectional view of the illustration in Fig. 5 taken on the line 6-6 of that figure. A

In practicing the invention a blank is rst formed by applying a coating of conducting mate-y rial of the desired resistivity on a tubular core made of an insulating material, for example a ceramic. The coating may be any suitable material such as carbon, and may be applied to the core in any suitable manner known to the art.

Blanks I0 of the type described with a conductive i plewood, N. J., assigner Company, Incorporated, New York, N. Y., a corporation of New York Application' J une 20, 1947, Serial No. 756,007

III

coating II are shown in different stages of the grooving process in the various figures of the drawing.

Each of Figs, 1, 2 and 3 shows a blank I0 held for rotation about its longitudinal axis in a pair of rotatable oppositely disposed chucks I2 and I3 which may be driven by any suitable source, not shown. A pair of insulating grooves I 4 and I5 may be spirally cut around the blank I0 either simultaneously-as illustrated in Figs. 1 and 2 or individually as in Fig. 3. In Fig. 1 the parallel grooves are shown being cut simultaneously by a dual cutting element 20 which may be a grinding wheel with a double-ridged periphery or a pair of cutting styluses, the object of course being to cut parallel spiral grooves deep enough to completely remove the conductive coating I I in the grooved area so as to form spirally extending insulating areas between parallel spiral conductive paths 2| and 22 in the coating II. The grinding wheel 20 is provided with twin cutting ridges 23 around its periphery and the wheel is iixed on a rotatable and axially movable shaft 24 which may be connected. to any suitable driving and control means, not shown.

In order to provide the desired pitch and spacing of the insulating grooves I4 and I5 there must be a relative longitudinal motion between the cutting elements 20 and the rotating blank. For example, in Fig. 1 the chucks I2 and I3, while rotating in the direction of the curved arrow I6 may be stationary with regard to longitudinal motion, and the cutting element 20 may progress longitudinally from left to right during the groove-cutting process. A similar relative movement between the cutting elements and the rotating blank is required in practicing the methods illustrated in Figs. 2 and 3.

In Fig. 2 a pair of oppositely disposed cutting elements 30 and 3l, one on each side of the rotating blank I0, are used to simultaneously cut the two separate grooves Il and I5, one cutting element being provided for each groove.

Fig. 3 illustrates a method whereby the single cutting element grooves; iirst one groove is completed as desired and then the cutting element may be returned to the position shown in Fig. 3 to begin cutting a second'groove parallel to the one previously out.

To -maintain an electrical connection between the ends of the spiral conducting paths 2| and 22 at one end of the formed blank, the grooving operation is stopped short at that end of the blankthereby leaving a conducting path of the coating II between the parallel conductive paths 20 may be utilized to cut both 2| and 22 as shown at the right end of the completely grooved blank in Fig. 4. When the grooving operation is completed, one end of the processed blank I may be ground of! as shown at the left end of the processed blank illustrated in Fig. 4 to separate the ends of the conducting paths 2| and 22 at that end of the processed blank.

The processed blank I0 may be completed as a practical non-inductive resistor by securing terminal connections 32 and 33, such as wire pigtails or metal strips, to the ground end of the processed blank so as to effect an electrical connection between the terminals 32 and 33 and the ends of the conducting paths 2| and 22. The connecting terminals 32 and 33 may be held xedly in place by an insulating cap 34 firmly iltted on the end of the completed resistor as shown in Fig. 5.

The resistor will be substantially non-inductive because an electrical current entering one connecting terminal will travel through one spiral conducting path and then double back through the parallel spiral conducting path thereby substantially cancelling inductive effects.

What is claimed is:

l. A method of making an electrical resistor comprising applying a conductive coating on a cylindrical insulating base, cutting a plurality of spiral grooves through said conductive coating, said grooves extending helically around said base and the helixes of one groove arranged between the helixes of the adjacent groove to form a plurality of parallel spiral conducting paths separated by spirally extending insulating areas, stopping said grooving short of one end of the base to provide a conductive connection between said paths at said one end of the base, and connecting electrical terminals to the other ends of said spiral conducting paths.

2. A method of making an electrical resistor comprising applying a coating of conductive material on a cylindrical insulating base and cutting simultaneously a plurality of parallel insulating grooves through said conductive coating and into said base, said grooves extending spirally around said base thereby separating said conductive coating into a plurality of parallel spiral conducting paths extending helically around and throughout an identical substantial part of the length of said base.

3. A method of making an electrical resistor comprising applying a conductive coating on a cylindrical insulating base, cutting a spiral groove through said conductive coating and into said base, and cutting a second groove parallel to said rst groove through said conductive coating and into said base, said grooves extending helically around said base and along an identical substantial part of thelength of said base to separate said conductive coating into two parallel spiral conducting paths.

4. An electrical resistor comprising a cylindrical insulating base, a conductive coating on said base, a plurality of spiral grooves cut through said conductive coating along an identical substantial portion of the length of said base, said grooves extending helically around said base to form spirally extending insulating areas separating said conductive coating into a plurality of conductive paths interconnected at one end.

5. An lelectrical resistor comprising a cylindrical insulating'base, a conductive coating on said base, a Pluralityof spiral grooves cut through said conductive coating and into said base, said grooves extending helically around said base along an identical portion thereof to form spirally extending insulating areas separating said conductive coating into a plurality of conductive paths connected together at one end of said base, and electrical terminals secured to said resistor for making electrical contact with the ends of said conducting paths at the other end of said base.

6. The method of making an electrical resistor including the steps of providing insulating areas in a conductive-material coated substantially cylindrical insulating base to separate the con= ductive material into a plurality of spiral conducting paths connected together at one end and extending helically around said base throughout an identical substantial part 0f the length thereof, and providing electrical connections to the separated ends of said conducting paths.

'7. A non-inductive resistor vcomprising an insulating base, a coating of conductive material on said base, said coating being divided into two spiral parallel conducting paths separated by an insulating area extending spirally around said coated base along an identical portion thereof. said conducting paths being electrically connected together at one end, and electrical terminals connected to the free ends of said conducting paths. 8. A method of making electrical resistors comprising applying a coating of conducting material on a substantially cylindrical insulating base and separating said coating into a plurality of parallel spiral conducting paths extending helically around said base throughout an identical substantial part thereof.

9. A method of making an electrical resistor comprising applying a coating of conducting material on a substantially cylindrical insulating base and separating said coating into a plurality of parallel spiral conducting paths extending helically around said resistor by cutting a plurality of grooves through said coating, said grooves extending helically around said base throughout an identical substantial portion of the length thereof.

10. A method of making electrical resistors comprising applying a coating of conductive material on a substantially cylindrical insulating base, separating said coating into a plurality of spiral conducting paths-connected at one end and extending helically around said base and along a substantial part of the length thereof by cutting a plurality of spiral grooves through said coating, said grooves extending helically around said base throughout a substantial part of the length of and intermediate the ends of the base, and grinding away a portion of the base and its coating at one end to completely insulate the paths one from the other at that end.

11. A method of making electrical resistors comprising applying a conductive coating on a cylindrical insulating base, cutting a plurality oi spiral grooves through said conductive coating, said grooves extending helically around said base along a substantial part of the length thereof and inter-mediate the ends thereof to form a plurality of parallel spiral conducting paths intermediate the ends of said base and separated by spirally extending insulating areas, and removing a portion of the conductive coating from one end of said base to completely insulate said conducting paths one from the other at that end of the base.

12. A method of making electrical resistors comprising applying a conductive coating on a cylindrical insulating base, cutting a plurality oi' parallel spiral grooves through said conductive coating.' said grooves extending helically around said base along a substantial part of the length thereof and intermediate the ends thereof to form a plurality of parallel spiral conducting paths intermediate the ends of said base and separated by spirally extending insulating areas, removing a portion of the conductive coating from one end of said base to completely insulate said conducting paths one from the other at that end of the base, and connecting electrical terminals to the separate conducting paths at said one end.

13. A method of making an electrical resistor comprising applying a coating of conductive material on a cylindrical insulating base, cutting simultaneously a plurality of parallel insulating grooves through said conductive coating, said grooves extending spirally around said base and along a substantial part of the length thereof and intermediate its ends thereby separating said conductive coating into a plurality of parallel spiral conducting paths extending helically around and throughout a substantial portion of the length of said base and intermediate the ends thereof, and removing a portion of the conductive coating from one end of said base to completely insulate the said conductive paths one from the other at that end.

14. A method of making electrical resistors comprising applying a conductive coating on a cylindrical insulating base, cutting a spiral insulating groove through said conductive coating around and along a substantial part of the length of said base, stopping the grooving short of the one end of the said base, cutting a second insulating groove parallel to and coextensive with said first groove through said conductive coating. said grooves thereby dividing said conductive coating into two parallel spiral conducting paths conductively connected at one end and extending helically around and throughout a substantial part of the length of said base.

15. A method of making electrical resistors comprising applying a coating of conducting material on a substantially cylindrical insulating base and separating said coating into a plurality of spiral conducting paths extending helically around said base with the helixes of one spiral path arranged between the helixes of the adiacent spiral path.

DE HART G. SCRANTOM.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,294,607 Boardman Feb. 18, 1919 1,635,184 Jones July 12, 1927 2,330,782 Morelock Sept. 28, 1943 

